There is some info in Hugh's book Straight and True - some of which is from a very old tome which is actually about heraldry, but in which the author moves on from the charges on escutcheons to details of these items in real life. It is a difficult tome (and I use that word advisedly) to get hold of and even more difficult to find what you want inside it. It is called "The Academy of Armoury" by Randall Holme III privately printed in Chester 1688